Europa Mission

[Zinjanthropos]

Was checking in on the Europa Clipper Mission scheduled for 2024 when I found this great NASA site which contains the answers to a lot of questions we might have. One question I have is how does a planet encased in an icy shell form? Trying to imagine a gigantic blob of water behaving like a snowflake/raindrop drifting through space. You see videos of astronauts creating small wriggling masses of H2O in the spacecraft and I can't help but think that's how an iceball planet might have looked like.

[Catastrophe]

Was checking in on the Europa Clipper Mission scheduled for 2024 when I found this great NASA site which contains the answers to a lot of questions we might have. One question I have is how does a planet encased in an icy shell form? Trying to imagine a gigantic blob of water behaving like a snowflake/raindrop drifting through space. You see videos of astronauts creating small wriggling masses of H2O in the spacecraft and I can't help but think that's how an iceball planet might have looked like.

Catastrophe wrote:

Pardon my ignorance, but I do not fully understand the question.
Whilst Europa has an icy shell, you are asking about such shell formation on planets and not satellites. The only candidate planets are Uranus and Neptune. Wiki on ice giants gives:

QUOTE
Although the ice giants also have hydrogen envelopes, these are much smaller. They account for less than 20% of their mass. Their hydrogen also never reaches the depths necessary for the pressure to create metallic hydrogen.[1] 
QUOTE

. . .   . . .   . . .   from which it seems to me that they cannot form icy shells outside the hydrogen envelopes.
https://solarsystem.nasa.gov/moons/jupit.../in-depth/ gives !"the moon’s ice shell, where the ice makes contact with the ocean."
I stand to be corrected on this point.

[Catastrophe]

If it is of any interest, there is a very detailed article on Europa's icy shell:
Geodynamics of Europa’s Icy Shell Francis Nimmo University of California Santa Cruz Michael Manga University of California Berkeley
Geodynamics of Europa's Icy Shell - Earth and Planetary ...
www.es.ucsc.edu › ~fnimmo › website › draft5
Europa's icy shell records a complex tectonic history that reflects an interaction between surface processes, internal structure, and orbital dynamics. The icy shell ...
by F Nimmo - ‎Cited by 44 - ‎Related articles
Some brief extracts:
There are two overarching questions on which we focus: (1) What are the origins of the observed surface features? (2) What do the characteristics of surface features tell us about the properties and evolution of the icy shell?
In order to answer these questions, the first two parts of this chapter will consist of theoretical explorations of the likely structure of a floating icy shell, and the different mechanisms available to deform the shell and leave a tectonic record on the surface. Section 4 will then compare these theoretical predictions with observations of Europa’s surface to infer the present-day characteristics of the icy shell. Section 5 will carry out a similar exercise focusing on the evolution of the icy shell through time. Section 6 will conclude with a review and suggestions for future work.
Coupled thermal-orbital evolution models can be used to investigate whether a thickening icy shell is likely, and the timescales over which any thickening occurs, but such models are complicated.  (Section 5 my emphasis.)


The simple answer is formation of an icy shell on a saline ocean.

[C C]

[...] Trying to imagine a gigantic blob of water behaving like a snowflake/raindrop drifting through space. You see videos of astronauts creating small wriggling masses of H2O in the spacecraft and I can't help but think that's how an iceball planet might have looked like.

Thanks to Catastrophe for reviving this neglected topic.

A theory that apparently wasn't published yet back in February proposes that the largest moons of Jupiter may have formed from a gradual accumulation of icy grains ("hail") and dust that Jupiter attracted and trapped in orbits around it. So Europa was arguably never a blob of water in space (liquid or frozen-ish). Although its ocean is deeper than Earth's, it is still mostly rocky interior and a metallic core. According to this model, the moon was built-up gradually in the course of circa a thousand years, and presumably the water separated and seeped up via the heated disturbances below.

Io formed first, then Europa, then Ganymede, and finally Callisto -- but the latter taking millions of years longer because the material around Jupiter was more depleted. Europa and Io have more geological activity due to their tidal heating. Callisto lacks such gravitational influences upon it because it isn't part of the orbital resonance of the other three moons; Ganymede is possibly too far out to experience the degree of what Io and Europa do.

A new model offers an explanation for how the Galilean satellites formed around the solar system’s largest world.
https://www.nytimes.com/2020/05/18/scien...uropa.html

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[...] One question I have is how does a planet encased in an icy shell form?

If it is of any interest, there is a very detailed article on Europa's icy shell [...] The simple answer is formation of an icy shell on a saline ocean.

Some scientific literature published back in the 1970s speculated that Europa might have had a liquid surface in the first few million years after its formation. Thus, the ice covering forming later as the outer temperatures dropped rather than, say, vice versa (melting underneath occurring and a liquid subsurface ocean arising, leaving the still frozen surface and its shifting geological activity). But after all the space probe data and computer simulations that ensued for decades, not sure if such has decreased or enhanced the possibility of a completely liquid ocean in the beginning. Alternative might even be a scattered mix of the two in the earliest era, liquid and frozen micro spots and branching veins throughout the depths of the "ocean".

[confused2]

If it is of any interest, there is a very detailed article on Europa's icy shell:

Sorry the link didn't work for me.
I did find:-
https://agupubs.onlinelibrary.wiley.com/...03JE002103

[Image: jgre1739-fig-0001.png]

Arthur C Clark got there long before me - it looks like the kind of trails things leave in the garden as they hunt, visit and pass through. I am not for a moment (of course) suggesting life on Europa but..a totally inorganic search for old and new weaknesses and fault lines could mimic the activities of sentient beings. Or.

[Zinjanthropos]

I think I understand 2001 Space Odyssey a lot more now. 

Couple weeks ago I watched a Netflix movie about humans landing on Europa. Can’t remember the name but crew got killed off one by one and not until the movie’s end was Earth contacted with a fleeting glimpse of some tentacled critter. Also the ice the craft landed on was thin in some spots and some crew and spaceship eventually fell in thru the cracks. Would there be a chance of thin ice anywhere on Europa?

[Catastrophe]

Catastrophe comments:

Thickness of ice on Europa is a hot topic.

New measurements of impact crater topography show that Europa has a thick ice shell
Europan Pizza:Thin Crust or Thick Crust?

https://www.lpi.usra.edu/resources/europa/thickice/

A detailed article with particular reference to effect on life. Thin ice is good for photostnthesis but bad for radiation effects.

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Thick or Thin Ice Shell on Europa? – NASA's Europa Clipper

[/url]

europa.nasa.gov › resources › thick-or-thin-ice-shell-on...


8 Jul 2017 - Scientists are all but certain that Europa has an ocean underneath its icy surface, but they do not know how thick this ice might be.

In general the ice is not stable in the long term (astronomical context) and thin ice can be brought about by diverse mechanisms. There are even reports of 'lakes' in the ice between the surface and the underground ocean.

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Catastrophe comments:

Thickness of ice on Europa is a hot topic.

New measurements of impact crater topography show that Europa has a thick ice shell
Europan Pizza:Thin Crust or Thick Crust?
https://www.lpi.usra.edu/resources/europa/thickice/
A detailed article with particular reference to effect on life. Thin ice is good for photostnthesis but bad for radiation effects.

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Thick or Thin Ice Shell on Europa? – NASA's Europa Clipper
[url=https://europa.nasa.gov/resources/36/thick-or-thin-ice-shell-on-euro]https://europa.nasa.gov/resources/36/thick-or-thin-ice-shell-on-euro
8 Jul 2017 - Scientists are all but certain that Europa has an ocean underneath its icy surface, but they do not know how thick this ice might be.

In general the ice is not stable in the long term (astronomical context) and thin ice can be brought about by diverse mechanisms. There are eben reports of 'lakes' in the ice between the surface and the underground ocean.

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Sorry. Links are working but not going so well with formatting.
I will stick with Quick reply for the moment
Cat

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The presence of 'lakes' within the frozen crust obviously provides 'thin spots'.

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The answer is to ignore the blue bits (other than links). I obviously need to avoid repetition and hope to be literate soon.

[Zinjanthropos]

In general the ice is not stable in the long term (astronomical context) and thin ice can be brought about by diverse mechanisms. There are even reports of 'lakes' in the ice between the surface and the underground ocean.

Cat..... there is a "preview post" button you can hit before sending. You can look at it and see where your post needs editing. Anyways it's all good, we can see what you're trying to do. 

If there is an ocean under the ice of Europa is it possible that the water could be close to boiling point or at least at a very warm temperature. With the closeness of the gas giant tugging & pulling on this moon's inner core over the eons might water temperatures be even higher than Earth's on average but not hot enough at the ice boundary to cause any significant melting?

[Catastrophe]

Water temperature on Europa

Here is the key excerpt. I will put up the whole text:
QUOTE
Europa is in its own little habitable zone around Jupiter. It's not too close, which would turn it into a volcano extravaganza like Io, and not too far, which would leave it cold and unchanging like Callisto. Europa is warm, but not too hot. Water liquefies, but doesn't evaporate.
QUOTE

https://www.space.com/34216-under-the-ic...uropa.html
What's Going on Under the Ice of Europa?
By Paul Sutter September 28, 2016

Thank you for your kind assistance  Cat

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confused2

I am having problems with that link too. If you put the following into Google, you should locate it immediately. If I do get the link working I will post it for future reference  Cat

Geodynamics of Europa’s Icy Shell
Francis Nimmo University of California Santa Cruz
Michael Manga University of California Berkeley

[Catastrophe]

confused2  Here is an alternative link to the same paper:

https://www.researchgate.net/publication..._Icy_Shell

I have checked this works. You need to scroll down below the graph.
Sorry about the first one. It just refuses copy and paste, and everything else I throw at it.